1. Field of the Invention
The present invention relates to a color image data encoding apparatus, for encoding color image data obtained by a color original reader or a color television camera.
2. Related Background Art
In storage or transmission of image information, it has been customary to reduce the redundancy by suitable encoding in consideration of the efficiency. Such encoding has been principally developed for binary black-and-white or color image information.
However, there have been recently developed finer image information with multiple levels, including multi-level color image information.
Consequently, as encoding process has become necessary also for such multi-level color image information. So far, such encoding has been made by applying the conventional black-and-white encoding process to each of three primary colors of red, green and blue, by digitization utilizing correlation of three primary colors in each pixel.
However the former process mentioned above is naturally inefficient and often causes errors in color registration. The latter process is relatively free from errors in color registration, but cannot be efficient because it strongly relies on the correlation of the primary colors.
On the other hand, in certain equipment such as facsimile, electronic file or copying machine, it is often required to effect a conversion of luminosity or color on the data transmitted or stored in a buffer memory or the like. In such case, a conversion on the encoded data is desirable in consideration of efficiency. However the conventional encoding processes do not allow direct conversion of the encoded color image data.
For example in a facsimile system, such requirement has been resolved by sending the information on such conversion from the receiver to the transmitter, which in response resends the data after such conversion. Such solution naturally requires an increased time and complicates the mutual communication between the transmitter and the receiver. Also in an electronic file or the like, in which such solution is not available, the encoded data have to be decoded before the required conversion can be made. Such process results in deterioration of image quality due to the repeated processes and requires an additional working memory, so that the advantage of employing encoded data cannot be fully exploited.